A bar coater and a method for keeping the coating-bar cradle comprised therein clean

Abstract: The invention concerns a method for keeping the coating-bar cradle in a bar coater clean in a bar coater in which the coating bar is substantially over its entire length supported revolvingly in a bar cradle (18) fixed to the frame of the coater, which cradle is provided with one or several water grooves (5) substantially parallel to the coating bar and open towards said coating bar. According to the invention, at least one of the water grooves (5) in the bar cradle (18) is kept open constantly and forcibly by promoting the flow in the water groove (5) by means of negative pressure connected to the outlet side of the water. The invention also concerns an equipment by whose means the cradle of the coating bar is kept clean constantly.

Description: The invention concerns a method for keeping the coating-bar cradle in a bar coater clean in a bar coater in which the coating bar is substantially over its entire length supported revolvingly in a bar cradle fixed to the frame of the coater, which cradle is provided with one or several water grooves substantially parallel to the coating bar and open towards said coating bar. The invention also concerns a bar coater in which the coating bar is substantially over its entire length supported revolvingly in a cradle fixed to the frame of the coater, which cradle is provided with at least one water groove substantially parallel to the coating bar and open towards said coating bar. Bar coaters are used in the coating of paper in particular in cases in which it is feared that the coating blade in a blade coater produces streaks in the paper face. At present, especially in size presses, bar coaters have proved very good and usable, because by their means the size film can be metered well onto the roll faces in the size press. The coating bars in bar coaters may be either grooved or smooth-faced. A coating bar is, as a rule, rotated in the sense opposite to the running direction of the web, the object of said rotation being complete elimination of said streaks occasionally associated with the use of blade coaters. The speed of rotation of the bar is, as a rule, 10...600 revolutions per minute. This is why the coating bars are provided with a suitable drive gear to rotate the bar, and in wide machines the bars are usually provided with drives at both ends of the bar so as to avoid torsional oscillations. When a bar coater is used, the coating process itself can be arranged, for example, so that the coating agent is applied to the web face by means of an applicator roll, and any excessive coating agent is doctored off the web face by means of the coating bar. A bar coater may also be constructed as a so-called short-dwell unit, in which the coating agent is introduced into a coating-agent chamber, which is defined by the front wall of the chamber and, on the other hand, by the coating bar and by the base to be coated itself, which base may be the face of a size-press roll, the face of a back-up roll, the paper web, or equivalent. As a rule, the coating bar is mounted as revolving in a cradle made of a suitable material, for example polyurethane. The bar is normally supported in said cradle over its entire length. In the cradle, in connection with the bar, as a rule, a water groove or water grooves is/are provided, the water circulating in said groove(s) being supposed to lubricate, to cleanse, and to cool or to heat the coating bar. The number of the water grooves is usually one or two. However, a substantial problem in bar coaters is blocking of the water groove by size or pigment-coating paste. On occurrence of blocking, the cooling, washing and lubricating effect of water is discontinued, and at the same time the water penetrates onto the coating base. In view of solving the above problem, i.e. the blocking of the water groove with the resulting detrimental effects, in the applicant's FI Patent No. 83,598 of earlier date, a method and an equipment are described by whose means the water groove is kept open and clean forcibly by means of a mechanical operating mechanism. Even though, by means of the solution in accordance with said publication, the desired goal is substantially achieved, the construction of the equipment intended for carrying out the method of the patent is complicated, quite expensive, and spacious. Moreover, the method and the device of the FI Patent 83,598 are rather difficult to control. The object of the present invention is to provide a method and a bar coater by whose means the drawbacks involved in the prior-art solutions are avoided. In view of achieving this, the method of the present invention is mainly characterized in that at least one of the water grooves in the bar cradle is kept open constantly and forcibly by promoting the flow in the water groove by means of negative pressure connected to the outlet side of the water groove. On the other hand, the bar coater in accordance with the invention is mainly characterized in that a vacuum pump is connected to the water groove to the side of the outlet flow of water, which pump is fitted to produce negative pressure in the water groove so as to promote the water flow and to prevent leakage of water out of the water groove. It is the most essential and most remarkable advantage of the present invention over the prior-art solutions that, according to the invention, in a way that is quite simple to carry into effect, the water groove in the cradle of the coating bar is kept open constantly so that blocking and interference arising from same in the operation of the machine do not occur. Thus, by means of the invention, the production stops involved in the prior-art equipments are avoided, the economic losses resulting from said stops being highly significant. The further advantages and characteristic features of the invention come out from the following detailed description of the invention. In the following, the invention will be described by way of example with reference to the figures in the accompanying drawing. Figure 1 is a schematic sectional side view of a bar coater. Figures 2 and 3 are fully schematic illustrations of alternative solutions for keeping the water groove in the coating-bar cradle in a bar coater as shown in Fig. 1 clean. In Fig. 1, the coating device is denoted generally with the reference numeral 10. The coating device 10 is a bar coater, whose coating bar 13 is, in the embodiment of Fig. 1, arranged against the paper or board web W running on the face of the back-up roll 14. The coating device 10 of the embodiment as shown in Fig. 1 is a coating device of the so-called short-dwell type, in which the coating agent is introduced into a coating-agent chamber 11 placed before the coating bar 13, in the running direction of the web W, which chamber 11 is, besides by said coating bar 13, also defined by the web W, by the front wall 12 of the coating-agent chamber, and by lateral seals (not shown). In the conventional way, the coating-agent chamber 11 is pressurized, and overflow of the coating agent is arranged out of the chamber 11 through the gap 15 between the front wall of the coating-agent chamber and the web W. The coating bar 13 is fitted revolvingly in a cradle 18 made of a suitable material, for example polyurethane, which cradle supports the coating bar 13 over its entire length. The coating bar 13 is provided with a purposeful drive gear (not shown), by whose means the coating bar 13 is rotated in the sense opposite to the running direction of the web W. The cradle 18 of the coating bar 13 is fitted in a support 16, and both the cradle 18 and the support 16 are together attached to a holder 19 mounted on the frame of the coating device 10. Moreover, in the support 16, underneath the cradle 18, a loading hose 17 is fitted, by whose means the coating bar 13 can be loaded in the desired way against the web W. Into the cradle 18, water grooves 5,6 have been formed, which are in connection with the coating bar 13 and which are open towards the coating bar 13, the water circulating in said grooves being supposed to lubricate, to cleanse, and to cool the coating bar 13. The object of the invention is to be able to keep especially the water groove placed in the cradle 18 and denoted with the reference numeral 5 constantly open. Figs. 2 and 3 in the drawing show some alternative exemplifying embodiments, by whose means the objectives of the invention can be achieved. Fig. 2 is a fully schematic illustration in the machine direction of a part of the cradle 18 of the coating bar and of a bar coater in accordance with the invention connected with the cradle. In the embodiment of Fig. 2, the keeping of the water groove 5 in the bar cradle 18 open has been accomplished so that, in one end of the water groove 5, means have been provided for feeding water into the water groove 5, and to the opposite end of the water groove 5, at the outlet side of the water, means have been connected by which the water is sucked out of the water groove 5 by means of negative pressure. In the illustration of Fig. 2, the means for feeding the water into the water groove 5 comprise a tank 21, which communicates with the water groove 5 through the duct 20. The tank 21 is placed at a level higher than the water groove 5, so that the water w contained in the tank 21 is carried into the water groove 5 by the effect of hydrostatic pressure. In the figure 2, it is also indicated by means of a dashed line that the duct 20 may be provided with a valve 22, by whose means the flow of water w into the water groove 5 can be regulated. Differing from Fig. 2, the feed of water into the water groove 5 can also be arranged from a pressure water network (not shown), from which the desired flow quantity can be taken by means of a valve. In the embodiment shown in Fig. 2, a vacuum pump 24 has been connected to the water groove 5 to the outlet side of water by means of the duct 23, water being sucked out of the water groove 5 by means of the negative pressure produced by said vacuum pump. The vacuum pump 24 produces a negative pressure in the water groove 5, which negative pressure prevents leakage of water w out of the water groove 5 between the coating bar 13 and the sealing lip of the bar cradle 18. By means of the vacuum pump 24, it is also possible to regulate the water w flow in the water groove 5 by adjusting the negative pressure produced by the vacuum pump 24. It is also possible to suck water out of the water groove 5 by means of hydrostatic negative pressure. Fig. 3 shows an alternative embodiment of the solution in accordance with the invention. In the embodiment of Fig. 3, the means shown in Fig. 2 for the feed and removal of water, which were fitted at opposite ends of the water groove 5 in the illustration in Fig. 2, have been substituted for by a number of feed ducts 26,27 and outlet ducts 29,30 placed in the longitudinal direction of the bar cradle 18a, i.e. in the transverse direction of the machine. In the illustration in Fig. 3, the feed ducts 26,27 passing into the water groove 5a communicate with a common water supply duct 25, and correspondingly the outlet ducts 29,30 passing out of the water groove 5a communicate with a common outlet duct 28. Even though it is not illustrated in Fig. 3, it is, however, obvious that the outlet duct 28 is additionally connected, for example, with a vacuum pump 24 similar to that shown in Fig. 2, water being sucked out of the water groove 5a by means of the negative pressure produced by said pump. Moreover, in Fig. 3 it is indicated by means of dashed lines that the water groove 5a may be divided into separate compartments by means of partition walls 31, the water being fed into each of said compartments through separate feed ducts, and the water being sucked out of said compartments through separate outlet ducts. Fig. 3 shows just a small portion of a bar cradle 18a, but it is understood that, in the water groove 5a, over the length of the bar cradle 18a, there may be several compartments separated by partition walls 31. The arrangement of compartments can be accomplished, for example, so that the water groove 5a is divided into two parts by means of a partition wall 31 fitted in the middle in the transverse direction of the machine, in which case, the supply of water into, and its removal out of, these compartments can take place in the transverse direction of the machine from opposite ends of the bar cradle 18a. The cleansing of the water groove 5,5a can be intensified further so that, at the same time, for example, an agent is fed into the water groove that lowers the friction or promotes the keeping of the groove clean. Under easy circumstances and in the case of suitable coating agents, the cleaning of the water groove 5,5a can also be carried out by just feeding water, size or paste alone into the water groove 5,5a. However, it is the fundamental idea of the invention that the water groove 5,5a is kept open and clean constantly and forcibly by means of negative pressure produced into the groove. Besides the cleansing of the coating bar 13 and of the bar cradle 18,18a, the water may also have a function of cooling the coating bar 13 and the cradle 18,18a. On the other hand, a high temperature of water is advantageous because of lower resistance to flow. Also, certain coating agent qualities require a certain level of temperature, in which case a high temperature of water may contribute to prevention of solidification and clogging of the coating agent.

Claims: Method for keeping the coating-bar cradle in a bar coater (10) clean, in which the coating bar (13) is substantially over its entire length supported revolvingly in a bar cradle (18,18a) fixed to the frame of the coater (10), which cradle is provided with one or several water grooves (5,5a) substantially parallel to the coating bar (13) and open towards said coating bar, characterized in that at least one of the water grooves (5,5a) in the bar cradle (18,18a) is kept open constantly and forcibly by promoting the flow in the water groove (5,5a) by means of negative pressure connected to the outlet side of the water groove. Method as claimed in claim 1, characterized in that water is fed into the water groove (5,5a) from one or several points in the longitudinal direction of the bar cradle (18,18a), and correspondingly water is removed out of the water groove (5,5a) by means of negative pressure from one or several points in the longitudinal direction of the bar cradle (18,18a). Method as claimed in claim 2, characterized in that the water groove (5a) is divided by means of partition walls (31) or equivalent into separate zones in the longitudinal direction of the bar cradle (18a), water being fed into said zones and water being removed from said zones through separate feed and outlet ducts (26,27, 29,30), in which case the flow in each zone is free from any disturbance that might possibly be caused by the flows taking place through the other zones. Method as claimed in any of the preceding claims, characterized in that the negative pressure in the water groove (5,5a) is produced by means of one or several vacuum pumps (24) connected with the duct/ducts (23,29,30) at the outlet side. A bar coater (10) in which the coating bar (13) is substantially over its entire length supported revolvingly in a cradle (18,18a) fixed to the frame of the coater (10), which cradle is provided with at least one water groove (5,5a,6) substantially parallel to the coating bar (13) and open towards said coating bar (13), characterized in that a vacuum pump (24) is connected to the water groove (5,5a) to the side of the outlet flow of water, which pump is fitted to produce negative pressure in the water groove (5,5a) so as to promote the water flow and to prevent leakage of water out of the water groove (5,5a). A bar coater as claimed in claim 5, characterized in that the supply of water into the water groove (5,5a) is arranged from one or several points in the longitudinal direction of the bar cradle (18,18a), and correspondingly the removal of water from the water groove (5,5a) is arranged from one or several points in the longitudinal direction of the bar cradle (18,18a), each outlet duct (29,30) communicating with a source (24) of negative pressure. A bar coater as claimed in claim 6, characterized in that the water groove (5a) is divided by partition walls (31) into two or more zones, each of said zones being provided with supply of water and with removal of water taking place by means of negative pressure.

Inventors: RANTANEN RAUNO, RANTANEN, RAUNO
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21H25
IPC codes: D21H25